In tire curing presses center mechanisms are employed which include a shaping bladder which is inserted into the green tire as the press closes initially to shape the tire, and through which hot curing media, such as steam, is circulated under high pressure to cure the tire. Shaping bladders are open at the bottom and the lower edge or bead is held by a clamp ring assembly mounted on a hub. Bladders may also be open at the top with the top bead held by a clamp ring assembly mounted on a manipulating post. The curing media enters and drains from the bladder through the hub. Because of a relatively short service life, shaping bladders in tire presses must periodically be replaced.
The bottom or lower clamp ring assembly for the shaping bladder is normally threaded on the hub. The hub and ring assembly include cylindrical telescoping surfaces and axially facing annular surfaces with an O-ring or seal provided between the former, and a harder bumper ring provided between the latter. The purpose of the bumper ring is to prevent metal-to-metal contact at the axially facing surfaces and thus avoid seizure which might be brought on by thermal expansion or contraction of the parts. Because of the latter problem the cylindrical surfaces require a significant clearance necessary to install, for example, a cold lower clamp ring assembly over a hot tub. Such clearances are necessary since operating temperatures may range from 300.degree. to 400.degree. F. To wait for the hub to cool down would require an inordinate amount of down-time for the press and would be grossly energy inefficient. However, because of the required clearances the seals may become ineffective at such operating temperatures permitting what is known as "blow-by". This can lead to defective tires as well as other significant problems.
Also, such bumper rings are normally installed in shallow grooves in such axially facing surfaces. Such rings in what may be a short period of time become crushed and lose not only any sealing capability, but also may fail to function to prevent the noted metal-to-metal contact. Crushed bumper rings are not easy to spot.
An example of such prior art seal ring and bumper ring design is shown in prior U.S. patent of Anand P. Singh et al U.S. Pat. No. 4,527,946 issued July 9, 1985.